Improve documentation structure

[andypbarrett]

This is the start of reorganizing and completing the documentation for earthaccess.

I have reorganized the first page of the docs to show a bare-bones example of authentication, granule search and download, to get people started.

I will focus on user-guides for the API methods starting with:

• login
• search_datasets
• search_data
• download
• open

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📚 Documentation preview 📚: https://earthaccess--498.org.readthedocs.build/en/498/

[mfisher87]

Decisions from hack day;

• Break up the “Welcome” page to multiple pages
• Remove/summarize/link to license/LoS info
• Glossary -> User Guide Overview

[mfisher87]

TODO:

• [x] Add more contributing sub-items to nav
• [x] Remove duplicate contributing entry in user guide nav

4ffe156

[mfisher87]

TODO:

• [x] Update user guide pages with callouts that the pages are WIP.
• [x] Link to relevant how-tos from user guide

[mfisher87]

I just force-pushed to update commit messages to credit everyone in the breakout room. I think we should merge this tomorrow! Last call for reviews?

@betolink @asteiker @andypbarrett @ArieKnoester @botanical @mikala-nsidc

[mfisher87]

All, @asteiker asked for a chance to review, please hold off on merging until then.

[asteiker]

Also @andypbarrett @MattF-NSIDC These restructured docs are really fantastic - this is excellent work!! The organization is much improved and it really feels like the scaffolding is in place to easily build and continue to improve from here.